Indoor leisure facilities such as gyms and swimming pools reopened their doors in England on Monday following the easing of lockdown restrictions.
The second step of the government's roadmap allows people to attend the facilities on their own or in household groups.
Prime Minister Boris Johnson has urged the nation to "behave responsibly", with pubs and restaurants allowed to serve outdoors and non-essential shops able to reopen.
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"I'm sure it will be a huge relief for those business owners who have been closed for so long, and for everyone else it's a chance to get back to doing some of the things we love and have missed," Johnson said.
"I urge everyone to continue to behave responsibly and remember 'hands, face, space and fresh air' to suppress Covid as we push on with our vaccination programme."
Neil Randall, chief executive of Anytime Fitness UK, told Sky Sports News. "There was a bit of nervousness last night if I'm honest, it's a little bit like Christmas. We haven't been trading since December 20, which is obviously difficult for business owners.
"We've only really traded three of the last 12 months all told. It's fantastic to see everyone here today. All but two slots are booked for today, so that shows there's a real willingness for everyone to get back to health and wellness again."
Duncan Goodhew, who won a swimming gold medal at the 1980 Olympics, told Sky Sports News: "It's a great moment. We've gone from the bathtub, into the pool. We've got space to move now. It's not just about swimming, it's about my own health and fitness.
"Like many, who rely on swimming, it has been a long time and for people with joints and back problems, swimming is the only meaningful form of exercise. In addition the 'Learn to Swim' schemes have been closed, so you have a generation of children getting into the water for the first time."
In Wales, the reopening of gyms and leisure centres has been brought forward by a week to May 3, including for one-to-one training, although group exercise classes remain banned.
For Northern Ireland, from Monday outdoor sports training will be allowed for recognised clubs, in groups of up to 15, provided all indoor facilities except toilets remain closed.
Meanwhile, gyms and pools in Scotland could reopen on April 26, with First Minister Nicola Sturgeon expected to give more details in the coming weeks.
The easing of restrictions in England comes a fortnight after outdoor sports facilities such as tennis and basketball courts reopened, while organised adult and children's sport - including grassroots football - was also able to return.
From no earlier than May 17 in England, indoor adult group sports and exercise classes will also reopen, while limited crowds will also be allowed at sporting events.
In the meantime, the FA Cup semi-final between Leicester and Southampton FA Cup on April 18 will be run as a test event for the return of fans, while the upcoming World Snooker Championship will increase its capacity throughout the tournament as part of the government's pilot programme.